This disclosure is directed to methods and apparatus for generating, from medical image data of a subject from a functional imaging modality, a modified intensity projection image for display.
In the medical imaging field, several imaging schemes are known. For example PET (Positron Emission Tomography) is a method for imaging a subject in 3D using an injected radio-active substance which is processed in the body, typically resulting in an image indicating one or more biological functions. Other such functional imaging modalities are known, such as SPECT.
In such functional images, many important pathologies and anatomical structures appear as very high (or low) intensities. For example, a tumor in an FDG-PET image will often appear as a bright region.
A Maximum Intensity Projection (MIP) image is a useful way to visualize such medical images. Each pixel in a MIP is the maximal intensity along a ray orthogonal to the plane of the MIP. The resulting pixel values come from different depths along the rays and hence a MIP can be thought of as a simple form of 3D visualisation.
Maximum Intensity Projections (MIP) of PET data are commonly used by clinicians to provide an overview of the acquired data, facilitating rapid identification of potential lesions. However, when constructing a MIP, information regarding the position of the intensity along the axis of projection (i.e., depth) is lost. As such, it can be difficult to determine visually in which region of the body or organ the intensity is located. For instance, it may be difficult to determine whether a lesion located at the edge of the lung, is located in the lung, or in the ribs.
For example, FIG. 1.1 is a schematic illustration of a MIP from PET data (100). There are a number of organ regions visible (102, 104, 106, 108, 110) each having different uptake/intensity. In this simplified example, each organ broadly has the same uptake across the organ. There are also a number of hotspots (114, 116, 118). Two of these (116, 118) appear to be either on the periphery of the lung, on the rib, or in some nearby intervening tissue—it is difficult to tell from the MIP.
One solution to this problem, that is available in some medical imaging software packages, is to enable automatic navigation from an intensity in the PET MIP to its corresponding position in multi-planar reconstructed (MPR) views (i.e., axial, sagittal and coronal slices) of the PET overlaid on the corresponding CT data. This enables the clinician to correlate the location of the intensity in the PET image with the corresponding anatomical position in the CT.
One disadvantage of this approach is the additional user input required (i.e., to click on the intensity and read the fused MPR) which precludes a rapid, interaction-free, assessment of the MIP.
An alternative method that enables anatomical localization in a MIP is the generation of organ-specific MIPs, disclosed in US 2009/0129641. This approach uses organ segmentations derived from the CT to produce MIPs only of PET data located within these segmentations.
One disadvantage of this approach is that by restricting the view to an organ-specific MIP, the clinician is unable to assess body regions outside this organ segmentation.